1. Field of the Invention
The present invention relates, in general, to nanoscale powders, methods for their manufacture, and, more particularly, to post-processing of nanoscale powders.
2. Relevant Background
Powders are used in numerous applications. They are the building blocks of electronic, telecommunication, electrical, magnetic, structural, optical, biomedical, chemical, thermal, and consumer goods. On-going market demand for smaller, faster, superior and more portable products has demanded miniaturization of numerous devices. This, in turn, has demanded miniaturization of the building blocks, i.e. the powders. Sub-micron and nanoscale (or nanosize, ultrafine) powders, with a size 10 to 100 times smaller than conventional micron size powders, enable quality improvement and differentiation of product characteristics at scales currently unachievable by commercially available micron-sized powders.
Nanopowders in particular and sub-micron powders in general are a novel family of materials whose distinguishing feature is that their domain size is so small that size confinement effects become a significant determinant of the materials"" performance. Such confinement effects can, therefore, lead to a wide range of commercially important properties. Nanopowders, therefore, are an extraordinary opportunity for design, development and commercialization of a wide range of devices and products for various applications. Furthermore, since they represent a whole new family of material precursors where conventional coarse-grain physiochemical mechanisms are not applicable, these materials offer unique combination of properties that can enable novel and multifunctional components of unmatched performance. Commonly-owned U.S. Pat. No. 6,228,904, which along with the references contained therein is hereby incorporated by reference in full, teach some applications of sub-micron and nanoscale powders. Co-pending application Ser. No. 09/638,977, which is assigned to the assignee of the present invention and which along with the references contained therein is hereby incorporated by reference in full, teaches exemplary methods for producing high purity nanoscale materials and their applications.
In most applications, powders need to satisfy a complex combination of functional and processing requirements. Submicron powders in general, and nanoscale powders in particular fail to meet all these requirements. This invention is directed to address these limitations.
Nanoscale powders of various compositions can be produced using different methods. Some illustrative but not exhaustive lists of manufacturing methods include precipitation, hydrothermal processing, combustion, arcing, template synthesis, milling, sputtering and thermal plasma. Often, although not always, nanoscale powders produced by such manufacturing methods lead to powders that do meet all the requirements of an end user application. For example, some of the issues limiting the broad use of nanopowders include,
1. Nanoparticles tend to form agglomerates that in some ways behave like larger particles; there is a need for post-processing technologies that can recover the nanoparticles from such agglomerates
2. Nanoparticles tend to aggregate thereby making it relatively difficult to disperse them; there is a need for post-processing technologies that can enable ease in the formation of nanoparticulate dispersions in aqueous and non-aqueous solvents
3. Nanoparticles offer unusual combination of properties; however sometimes they are not used because they are not satisfactory in at least one of the matrix of performance desired for the application; there is a need for post-processing technologies that can enable improvement in the unsatisfactory performance at an affordable cost
4. Nanoparticles tend to adsorb significant levels of gases over their high surface areas; alternatively, the surface of nanoparticles are of a form that makes them incompatible with preferred solvents in specific applications; there is a need for post-processing technologies that can enable improvement in the surface state of nanoparticles to overcome these limitations
5. Nanoparticles tend to require very high pressures for compaction into products. This is in part because of agglomeration and/or high internal friction. Although such high pressures can be used to consolidate nanoscale powders, this technique is often limited to the preparation of thin sections due to very high internal residual stresses. Post-processing techniques are needed that can readily form nanostructured products.
6. Nanoparticles are difficult to process into components because of their unusual Theological and other properties. Post-processing techniques are needed that can enable reliable, reproducible, and affordable processing of nanopowders into components.
Hence, a variety of needs exist for techniques for improving selected features of sub-micron powders, and specifically nanopowders, to improve the performance of these materials in known applications, and to open up new applications that, until now, were impractical or impossible.
Briefly stated, the present invention involves the post-processing of nanoscale powders of oxides, carbides, nitrides, borides, chalcogenides, metals, and alloys are described. The powders are post-processed to improve their functional and processing characteristics thereby enabling their widespread use in commercial applications. Fine powders discussed are of size less than 100 microns, preferably less than 10 micron, more preferably less than 1 micron, and most preferably less than 100 nanometers. Methods for producing such post-processed powders in high volume, low-cost, and reproducible quality are also outlined.